Directed Self Assembly (DSA) is a rapidly maturing technology for advanced patterning for semi-conductor applications. DSA is based on the self-assembling properties of block copolymer (BCP) materials. It offers a low-cost route to very dense and regular patterns. It is expected that DSA will need to be combined with traditional lithography techniques.
Several approaches for DSA have been proposed to define regular line/space patterns, line/space patterns with some irregular nature, regular hexagonal hole patterns, or more irregular and sparser hole patterns. DSA can thus be regarded as a “chemical resolution enhancement technique”. Among all DSA morphologies, the cylindrical structures have attracted significant attention, due to the potential to achieve sub-20 nm contact holes on a sub-40 nm pitch, which exceeds the capability of any current single patterning lithography.
Specifically, in templated DSA, a grapho-epitaxy flow, a trench-like pre-pattern (or “template”) is printed by conventional lithography. In this confined template, the BCP material allows a cylindrical phase separation which results in sub-resolution hole patterns. The configuration of holes within each template depends on the shape and size of the particular template and the BCP periodicity. Templated DSA is mainly considered for application in via mask levels. The technique has a relatively feasible path for implementation with existing design flows. It has the potential to replace a multiple patterning method in which multiple exposures per layer will be needed in expense of edge placement errors, increasing tool and production costs.
The most critical challenges that need to be understood and controlled include CD and pattern placement accuracy, low defectivity, and how to implement DSA as a patterning method.
In J. Bekaert, J. Doise, R. Gronheid, J. Ryckaert, G Vandenberghe, G Fenger, Y. J. Her, and Y. Cao, “N7 logic via patterning using templated DSA: implementation aspects”, Proc. SPIE 9658, Photomask Japan 2015: Photomask and Next-Generation Lithography Mask Technology XXII, 965804 (Jul. 9, 2015); doi:10.1117/12.2196524, paragraph 4, a demonstration is disclosed of a double DSA patterning scheme.
For Logic N7 technology node and beyond, it is known that more than a single template DSA process is required in order to meet the complex high density and small pitch requirement. When double or multiple template pre-pattern trenches overlap each other to achieve small pitch, the next (e.g., 2nd) template DSA process can be influenced or jeopardized by any of the previous (e.g., 1st) template DSA contact holes. A similar problem can arise when performing pillar patterning. For instance, openings or pillar structures resulting from a first DSA process may appear in the pre-pattern trenches of the second DSA process, jeopardizing the success of the second DSA process.
There exists a need in industry for improved double or multiple DSA patterning processes.